Use of data collected at CHESS was particularly helpful in determining and refining the structure of l-exonuclease. The analysis shows the structure to be toroidal and model-building suggests that it can enclose its DNA substrate. Data collected at CHESS were also important in helping us to solve the structure of a complex of the Skn-1 protein from C. elegans with DNA. At present we have a model showing the DNA and about three-quarters of the protein. Refinement and further model-building is in progress.